Flash smelting is a pyrometallurgical process in which a finely ground feed material is combusted with a reaction gas. A flash smelting furnace typically includes an elevated reaction shaft at the top of which is positioned a burner where pulverous feed material and reaction gas are brought together. In the case of copper smelting, the feed material is typically ore concentrates containing both copper and iron sulfide minerals. The concentrates are usually mixed with a silica flux and combusted with pre-heated air or oxygen-enriched air. Molten droplets are formed in the reaction shaft and fall to the hearth, forming a copper-rich matte and an iron-rich slag layer. Much of the sulfur in the concentrates combines with oxygen to produce sulfur dioxide which can be exhausted from the furnace as a gas and further treated to produce sulfuric acid.
A conventional burner for a flash smelter includes an injector having a water-cooled sleeve and an internal central lance, a wind box, and a cooling block that integrates with the roof of the furnace reaction shaft. The lower portion of the injector sleeve and the inner edge of the cooling block create an annular channel. The feed material is introduced from above and descends through the injector sleeve into the reaction shaft. Oxygen enriched combustion air enters the wind box and is discharged to the reaction shaft through the annular channel. Deflection of the feed material into the reaction gas is promoted by a bell-shaped tip at the lower end of the central lance. In addition, the tip includes multiple perforation jets that direct compressed air outwardly to disperse the feed material in an umbrella-shaped reaction zone. A contoured adjustment ring is mounted around the lower portion of the injector sleeve within the annular channel, and can slide along the vertical axis. The velocity of the reaction gas can be controlled to respond to different flow rates by raising and lowering the adjustment ring with control rods that extend upwardly through the wind box to increase or reduce the cross-sectional flow area in the annular channel. Such a burner for a flash smelting furnace is disclosed in U.S. Pat. No. 6,238,457.
Known burners of this type are associated with disadvantages that can adversely affect their performance. These include failure to achieve maximal mixing of the feed material with the combustion gas to optimize oxygen efficiency within the reactor. In addition, such burners have limited range of velocity control to optimize the performance of the burner relative to the feed material.
For example, the adjustment ring has a tendency to become sticky or misaligned on the injector sleeve. In addition, the adjustment ring is prone to accretions, which lead to obstructions in the combustion gas flow path. Both of these problems are known to lead to poor mixing and skewing of the burner flame, which causes poor combustion.
The presence of the adjustment ring precludes the possibility of mounting additional devices which can further adjustably modify the gas flow characteristics independently of velocity. Devices such as adjustable swirl inducing components, turbulence generating components, shrouds, etc. cannot be incorporated into a conventional design. These devices are known from other combustion fields, and are known to improve mixing and plume characteristics, improving combustion.
It is a goal of the inventors to provide an improved burner for a flash smelting furnace or other applications using a pulverous feed material that provides better mixing, more optimal oxygen efficiency, improved control, and ease of maintenance.